Position responsive signal generator



Oct. 7, 1969' J. F. SCHUGT POSITION RESPONSIVE SIGNAL GENERATOR FiledJuly 8, 1966 OSCILLATOR FEEDBACK PATH SCHMITT TRIGGER DEMODULATOR H.F.OSCILLATOR ATTOE/VE'V United States Patent 3,471,844 POSITION RESPONSIVESIGNAL GENERATOR Joseph F. Schugt, 1206 Vanderbilt Ave., Niagara Falls,N.Y. 14300 Filed July 8, 1966, Ser. No. 563,873 Int. Cl. G08c 21/00;H01f 21/10 US. Cl. 340-196 8 Claims The present invention is concernedwith a position responsive signal generator and more particularly withone which is very sensitive to movements of a moveable member havingnarrowly spaced controlling portions.

It is quite old in the art to have two electromagnetic units Whose coresare separated by an air gap and which are inductively coupled with eachother, there being interposed in the air gap, a member which hasportions thereof which affect the transmission of flux through the airgap differently from other portions. With such an arrangement, themovement of the member affects the transmission of flux between theinductively coupled members. The output of the inductively coupledmember may be employed in various manners.

The drawback of previous arrangements of this type is that it has beendiflicult to confine the flux in the air gap to a relative narrow pathso that the sensitivity of the apparatus to the position of the movablemember has not been as great as might be desired. This is a drawbackespecially where it is desired to respond with great sensitivity to theposition of closely spaced flux controlling portions or where such amovable member is rotated at very high speeds.

An object of the present invention is to provide an apparatus of thetype referred to above which is extremely sensitive and which can detectvery small incremental movements of such a movable member.

A further object of the present invention is to provide such apparatusin which the movable member is in the form of a rotatable disc which canbe driven at relatively high speeds.

Broadly, these objects are accomplished by the provision of shieldingmeans around each core which shielding means confines the flux passagethrough the air gap to a relatively narrow path bounded by smallopenings in the shielding means. The shielding means not only extendsover the face of the coupled electromagnetic units but also surroundsthese units peripherally and bridges over the air gap so that the pathfor the flux is confined to a relatively narrow band. The shieldingmeans may also have longitudinal openings in the peripheral shielding tofurther confine the flux path.

I further employ in connection with my position responsive signalgenerator, an arrangement in which one coil is connected to a highfrequency source of power and in which the other coil unit coupledtherewith is coupled in a feedback relation to the source of power sothat the output of the high frequency source of power is modulated inaccordance with the position of the movable member.

Various other objects of the invention will become apparent from aconsideration of accompanying claims, specification and drawing, ofwhich FIGURE 1 is a schematic view of my position responsive signalgenerator including my improved inductive pickoif and the circuitassociated therewith;

FIGURE 2 is a perspective view of the coils of my inductive pickotf andthe mounting means therefor;

FIGURE 3 is a view showing the coil structure of FIG- URE 2 inassociation with a rotatable disc, the potting compound surrounding thecoils being shown in section and the mounting and shielding means beingshown partially in section;

FIGURE 4 is an exploded view of the coil structure and shielding meansof my inductive pickolf;

FIGURE 5 is a plan view of the rotatable disc of my inductive pickoff,the shaft therefor being shown in section; and

FIGURE 6 is a view similar to FIGURE 5 of a modified form of the movablemember of my inductive pickoff.

Referring first to FIGURE 1, the inductive pickoff broadly comprises acoil 11 which is energized from a high frequency source of energy andwhich is inductively associated with a pickup coil 12. Extending betweenthe two coils 11 and 12 is a rotatable disc 13 which is eithercontinuously rotated or moved in accordance with some condition which itis desired to sense.

As best shown in FIGURE 5, the disc 13, which is formed of a conductivemetal such as aluminum, has a plurality of teeth 14 which are narrowlyspaced about the periphery thereof. In the specific form shown, theteeth are uniformly spaced. The teeth 14 are designed to extend into theflux gap between coils 11 and 12 to retard the transmission of flux fromcoil 11 to coil 12.

Referring to FIGURE 1, coil 11 is connected to a high frequencyoscillator 15 having output terminals 16 and 17 and feed-back terminals18 and 19. The output terminals 16 and 17 are connected to coil 11 whilethe feedback terminals 18 and 19 are connected to coil 12. The feedbackconnection through terminals 18 and 19 is preferably of the regenerativetype so that when the coils 11 and 12 are inductively coupled, theoscillation of the oscillator is sustained. When, however, one of theteeth 14 is located in the air gap between the coils 11 and 12 so as tosuppress transmission of flux between the coils, the oscillator ceasesto oscillate. The on-off high frequency output resulting from acontinuous rotation of disc 13 is shown schematically at 23 where, itwill be noted, the amplitude of the output rises rapidly and thenabruptly disappears during the portion of the rotation of disc 13 inwhich one of the teeth 14 is interposed between the two coils 11 and 12.Each time when one of the teeth blocks the air gap, the magnitude of thehigh frequency voltage builds up again. The modulated output of theoscilator is connected through conductors 20 and 21 to a demodulator 22to remove the high frequency components therefrom. The demodulatedvoltage is shown by the wave form 25. The output of demodulator 22 isthen fed to a conventional Schmitt trigger circuit 27 to form a squarewave output depicted at 28. The resulting output is a series of sharplytriggered square wave pulses, the occurrence of which is dependent uponthe position of teeth 14 of rotatable disc 13 with respect to the airgap between coils 11 and 12. While the disc 13 is continuously rotated,the frequency of the pulses depected in diagram 28 is in a fixedproportion to the angular velocity of disc 13.

Referring now to FIGURE 2, it will be noted that the coils 11 and 12which are shown as being surrounded by potting compound are secured to abracket 30 of conductive material having a down-turned mounting ear 31through which extends an aperture 32 for mounting the coil structure ofthe inductive pickotf assembly. The relationship of coils 11 and 12 tothe mounting member 30 is best shown in FIGURE 3. Here, the pottingcompound is shown in section. Referring to FIGURES 2 and 3, the mountingmember 30 has a forwardly extending portion 33 of conductive materialacting as part of the shielding means and to which the coils 11 and 12and the rest of the shielding means, to be presently described, aresecured. In FIGURES 1 and 3, the position of the inductive disc 13 withrespect to coils 11 and 12 is shown. It will be noted that the inductivedisc 13 is secured in a suitable manner to a shaft 35 which is eitherdriven at a desired frequency or is positioned in accordance with somecondition which it is desired to sense.

An important feature of my invention resides in the shieldingsurrounding the coils 11 and 12. It will be noted that coils 11 and 12are surrounded by cylindrical shields 40 and 41. Shield 40 is shown ashaving a longitudinal. slot 42 extending the full length thereof andshield 41 is shown as having a similar slot 43 extending longitudinallythe full length thereof. Secured to the inner end of the annular sleeve40 is an end shield 45 having a slot 46 extending from the upper end ofthe shield downwardly to a point slightly below the lower edge of a core44 extending longitudinally through the coil 11. The width of slot 46 inthe end shield 45 is relatively narrow and corresponds in width to theslot 42 in the annular shield 40.

Associated with annular sleeve 41 surrounding coil 12 is an end shield49 having a slot 50 therein which likewise extends from the upper edgeof end shield 49 to a point slightly below the lower edge of a magneticcore 51 extending through the coil 12. Likewise, the slot 50 isrelatively narrow and of the same width as the slot 43 in the annularsleeve 41.

It will be noted that the end shield 49 is somewhat greater in verticalextent than the end shield 45, the end shield 45 having associatedtherewith a further shielding member 53 of conductive material in theform of a longitudinal strip spaced by a narrow air gap from the upperend of shield 45. The vertical extent of the end shield 45 and theconductive strip 53 is substantially the same as that of end shield 49,the upper end of end shield 49 being secured to the conductive arm 33 ofcoil support 30. Similarly, the conductive strip 53 is likewise securedin conductive relation to the conductive member 33. Conductive member 33thus acts to further confine the return flux from coils 11 and 12 to thenarrow zone which is controlled by the teeth 14.

Secured to the outer end of the annular shield 41) associted with coil11 is a plate 56 of insulating material having a plurality of conductivemembers 57 and 58 secured thereto. The ends of the conductive coil 11are secured to these conductive members 57 and 58 to provide theterminals for coil 11. Similarly, an insulating plate 60 havingconductive members 61 and 62 secured thereto is secured to the outer endof the annular shield 41 surrounding coil 12, the opposite ends of theconductor forming coil 12 being secured to the conductive members 61 and62 which constitute end terminals for coil 12. When assembled, bothcoils 11 and 12 are completely shielded except for the outer ends, thenarrow gap provided for flux by the slots 42 and 43, the slots 46 and 50and the narrow gap existing between conductive member 53 and the endshield 45. The entire unit is held in position by potting compound toproduce a unit similar to that of FIGURES 2 and 3. The potted coils andshield assembly is fastened to the conductor member 33 by a suitableadhesive such as an epoxy adhesive. The outer ends of the coils may alsobe shielded, but since this is less effective, the outer ends of thecoil assembly may remain unshielded as shown in the drawing.

While I have referred to the end shielding members 45, 49 and 53 asbeing made of conductive material, I have found it desirable in somecases to form the end shields 49 and the assembly of shielding members45 and 53 of copper clad insulating material such as fiber glass withthe copper etched away to form the slots 46 and 50 and the transverseslot shown between conductive strip 53 and end shield 45.

Also, while I have shown the annular shields 4t and 41 as being providedwith longitudinal slots 42 and 43, it is not necessary to have thelongitudinal slots extend to the outer ends of the annular shields 40and 41. In fact, these slots may be entirely omitted when the diameterof the annular shields is sufficiently great that the transverse slotbeneath the strip 53 is below the upper wall of the annular shield topermit the flux to re-enter the area around coil 11 within the annularshield 40.

Referring to the flux paths present, it will be noted that the majorportion of the alternating flux produced by coil 11 can pass out fromthe inward end of core 44 through the slot 46 back through thetransverse slot between strip 53 and the main portion of end shield.45,through the slot 42, and back to the outer end of core 44. Also, a smallportion of the flux will pass through the slot 50, the inner portion ofthe ferro-magnetic core 51, and back through the longitudinal slot 43,the slot 50, the transverse slot below strip 53, the longitudinal slot42, and back to the outer end of the core 44. This is the conditionwhich exists when no tooth 14- is in alignment with the slots 46 and 50.I have found it highly desirable to provide the transverse slot betweenstrip 53 and end shield rather than using merely an end shield likemember 49. The reason for this is apparently that the flux returningthrough the slot in end shield member 49 is forced downwardly andconfined in a vertical direction as it passes between the end shield 45and the shielding strip 53. It is then drawn together as it enters slot42. Thus a focusing action for the return flux is provided. If the endshield 45 is formed like shield 49, the flux would not be forced down tofacilitate its passage back into slot 42, and the flux path would not beas precisely controlled by the position of tooth 14.

It will be noted that ferro-magnetic core 44 is relatively short ascompared with ferro-magnetic core 51. The core 51 should be relativelylarge to provide as much induction coupling as possible. Core 44, on theoher hand, should be relatively small to reduce the high frequencylosses.

By confining the flux to the relatively narrow paths defined by slots42, 46, 43 and 50, the result is that the pickoif is extremely sensitiveto the position of the teeth 14 of the movable member 13. It thusbecomes possible to have an apparatus which is highly sensitive and yetdoes not require extremely small tolerances such as has been required byother inductive pickolfs. I am able to use an air gap of 0.1 to 0.12inch while obtaining the sensitivity that would otherwise necessitate anair gap of only .025 inch in the absence of the shielding with itsnarrow slots. Furthermore, with this structure, I am able to use aconductive disc 13 of approximately four inches in diameter and yetstill obtain pulses per revolution with high pulse rates as high asseveral thousand per second.

By employing the shielding construction just discussed, and by employinga Schmitt trigger or similar pulse shaping circuit it is possible toobtain with a very compact apparatus a large number of very sharppulses. As mentioned above, it is readily possible with this apparatusto obtain 6 sharp pulses per revolution of disc 13 at disc speeds whichwill result in pulse rates as high as ten thousand pulses per second.

While I have shown a disc having conductive teeth which are successivelybrought into the air gap, it is possible to employ a disc havingmagnetic teeth in which the flux transmission between the coils 11 and12 is increased rather than decreased when a tooth appears. I havefound, however, that far superior results are obtained by the use ofnon-ferrous conductive teeth to magnetic teeth. This is due to the factthat the insertion of a conductive shield, such as formed by a tooth 14has a much more marked effect upon the transmission of flux between theenergized and pickup coils than does the insertion of a magnetic tooth.In some cases, a small magnetic inlay of ferrous material in the centerarea of each of the non-ferrous metal teeth has been found to furtherimprove the control action of small control teeth.

While I have shown an oscillator 15 which only depends upon theinductive coupling between coils 11 and to initiate high frequencyoscillation by filtered-out, narrow pulses occurring at a relatively lowfrequency, e.g. at /s of the original oscillation frequency. This highfrequency oscillation will be sustained, however, only when a tooth 14is not in the air gap. Thus one will obtain a continuous high frequencyoscillation only during those portions of the rotation of disc 13 wherea tooth 14 is not present in the air gap.

MODIFICATION OF FIGURE 6 In FIGURE 6, I have shown a disc 70 formed ofinsulating material on which there are a plurality of conductivesegments 72. These can be applied by any of the techniques used inmaking printed circuits. The arrangement of FIGURE 6 is highlysatisfactory where excessive speeds of the disc and excessivetemperature variations are not encountered. If there are excessivetemperature variations or excessive speed the disc of FIGURE 6 may notprovide suflicient control action throughout the desired operationrange.

I claim as my invention:

1. A position responsive signal generator comprising: a plurality ofelectromagnetic units each having a core of magnetic material and awinding thereon, said cores having aligned portions with adjacent polefaces spaced apart to provide a narrow air gap therebetween, shieldingmeans surrounding each of said electromagnetic units, said shieldingmeans extending peripherally around each of said magnetic units exceptfor a single longitudinal slot in the shielding means for eachelectromagnetic unit extending for substantially the full length of saidelectromagnetic unit, said shielding means extending over the adjacentfaces of said electromagnetic units except for aligned relatively smallslots continuous with said longitudinal slots, and a movable memberhaving a part thereof movable through said air gap and having thereon aplurality of relatively small portions having a different effect on fluxtransmission through said air gap than the rest of said member so thatas said movable member assumes a position in which one of saidrelatively small portions extends between said aligned slots in saidshielding means, the inductive coupling between said electromagneticunits is abruptly changed.

2. The position responsive apparatus of claim 1 in which said relativelysmall portions on said movable member are portions of conductivematerial to reduce the transmission of flux through said air gap.

3. The position responsive apparatus of claim 1 in which the movablemember is in the form of a rotatable disc and in which said relativelysmall portions on said member are portions of conductive material onsaid member uniformly disposed radially from the center of said disc.

4. The position responsive apparatus of claim 1 in which the Winding ofone of said electromagnetic units is energized from an alternatingcurrent source of power and the other electromagnetic unit isinductively coupled therewith to an extent dependent upon the positionof said movable disc.

5. The position responsive apparatus of claim 4 in which the shieldingmeans for the electromagnetic unit coupled to said source has a furtherslot communicating with and transverse to said longitudinal and saidrelatively small slot in the shielding means for that electromagneticunit to provide a more precisely controlled flux path.

6. The position responsive apparatus of claim 1 in which the winding ofone of said electromagnetic units is energized from a high frequencysource of energy and in which the winding of the other electromagneticunit is coupled in feedback relation to said source to modulate theoutput thereof in accordance with the position of said movable member.

7. The position responsive apparatus of claim 6 in which the modulatedoutput of said source of energy is demodulated and employed to control atrigger circuit to generate pulses.

8. The position responsive apparatus of claim 1 in which there is afurther conductive shielding member bridging the air gap to furtherconfine the flux path between said coils.

References Cited UNITED STATES PATENTS 2,234,184 3/1941 MacLoren 340-1862,976,495 3/1961 Unger 336-84 3,064,191 11/1962 Dever 340196 THOMAS B.HABECKER, Primary Examiner US. Cl. X.R. 336-87

1. A POSITION RESPONSIVE SIGNAL GENERATOR COMPRISING: A PLURALITY OFELECTROMAGNETIC UNITS EACH HAVING A CORE OF MAGNETIC MATERIAL AND AWINDING THEREON, SAID CORES HAVING ALIGNED PORTIONS WITH ADJACENT POLEFACES SPACED APART TO PROVIDE A NARROW AIR GAP THEREBETWEEN, SHIELDINGMEANS SURROUNDING EACH OF SAID ELECTROMAGNETIC UNITS, SAID SHIELDINGMEANS EXTENDING PERIPHERALLY AROUND EACH OF SAID MAGNETIC UNITS EXCEPTFOR A SINGLE LONGITUDINAL SLOT IN THE SHIELDING MEANS FOR EACHELECTROMAGNETIC UNIT EXTENDING FOR SUBSTANTIALLY THE FULL LENGTH OF SAIDELECTROMAGNETIC UNIT, SAID SHIELDING MEANS EXTENDING OVER THE ADJACENTFACES OF SAID ELECTROMAGNETIC UNITS EXCEPT FOR ALIGNED RELATIVELY SMALLSLOTS CONDINUOUS WITH SAID LONGITUDINAL SLOTS, AND A MOVABLE MEMBERHAVING A PART THEREOF MOVABLE THROUGH SAID AIR GAP AND HAVING THEREON APLUALITY OF RELATIVELY SMALL PORTIONS HAVING A DIFFERENT EFFECT ON FLUXTRANSMISSION THROUGH SAID GAP THAN THE REST OF SAID MEMBER SO THAT ASSAID MOVABLE MEMBER ASSUMES A POSITION IN WHICH ONE OF SAID RELATIVELYSMALL PORTIONS EXTENDS BETWEEN SAID ALIGNED SLOTS IN SAID SHIELDINGMEANS, THE INDUCTIVE COUPLING BETWEEN SAID ELECTROMAGNETIC UNITS ISABRUPTLY CHANGED.